Dear all,I've just bought a little learner bike to take me upto my license exam. Itsa 124cc Hyosung Cruise II korean import (thing) that runs well and cheap. Myonly problem is that I need to do 5000 rpm just to reach 30 MPH on it (I doweigh in at around 120 Kilos).The engine seems to be powerfull enough to pull with lower revs (I caneasily start from zero in second gear) but the total speed reduction infirst gear is 30.5 to 1! - seems better suited to hauling caravans thancruising, at the moment..The wheel sproket has 48 teeth and is much larger than the chain-drivesproket and so I was wondering if reducing the wheel sproket to 38 teeth(with new diameter to suit) would be a sensible way to get a better top-endand a lower-rev cruising speed?.If I'm right on this (and I'm no mechanic - but I am an engineer), cananyone suggest a dealer where I can buy such an OEM sproket and maybe haveit fitted?Any other thoughts on squeezing a little more power out of it (withouthaving to drill-out the chamber and rebuild the engine..)?Any serious advice would be appreciated.Tony.

Bavanar appear to be the largest importer and they do offer a slightlybigger drive sprocket (1 tooth extra) - I will ask J&S for a larger gear

but

I doubt if they will be able / willing to supply it. If all else fails,

I'll

get the mech. eng. department techies here to cut me a new one.I will probably keep the bike for life if I can set it up so that it

cruises

comfortably because my wife wants to learn too, and when she's done,

we'll

probably drive it to our place in Spain and leave it there for the

kids..

You mention that it is a restricted bike, any idea how it can bede-restricted? - I will be taking my license test soon and will be

entitled

to drive a bike of upto 33 BHP (it currently outputs less than 14).I note from the manual that the exhaust is designed to comply with

strict

korean noise laws (71 dB Max) and as such is extremely quiet; would

removing

some of the piping within improve power at the cost of a little extra

noise?

I've also learnt that is has a very simple pulsed electronic ignitioncontroller that sets two different firing times for the engine when the

revs

are below 2200 and above 4000 rpm; I might look into programming amicrocontroller to take the pulses from this and speed-up / retard them

as

necessary, to improve performance (its just a hobby with me).Once again, thanks for the input. Being technically minded, I get as

much

satisfaction from learning about the mechanics involved as I do from

riding

the bike!

It's not a wildly powerful bike to begin with. Being a learner bike,it's limited in horsepower, but trying to get a single-cylinderfour-stroke engine with only two valves per cylinder to produceappreciably more than 100hp/litre (ie: 12.5hp) will involve a helluvalot of work for very little reward. It may put out a claimed 14hp, butin the real world.....Gearing it up *may* allow it to cruise at slightly reduced revs, butthere's likely to be a penalty in that you'll need to change down gearmore often to maintain momentum, and it *may* not pull the higher topgear into a strong headwind.To give you an idea, the long-running SOHC Honda 125 singles were onlyever capable of about 70mph flat out - and flat out, in these cases,means a skinny rider, in racing leathers, lying prone on the bike,with one hand clutching the fork leg....Given that, a top speed of 65mph sitting up, or in a slight crouch, isabout as good as you're ever going to get.Play with the gearing if you wish, but you are very unlikely to beable to make any worthwhile improvement to power and performance. Ireally wouldn't bother trying, beyond trying a simple sprocket changeas you are considering.Play with the gearing if you wish, but you are very unlikely to beable to make any worthwhile improvement to power and performance. Ireally wouldn't bother trying, beyond trying a simple sprocket changeas you are considering.

The sprocket and emptying out the exhoust a bit is really all I'mconsidering.The bike is a 4 valve single cylinder that is capable (I am discretelyinformed) of at least 18 hp but is severly restricted for UK use (most of itis in the exhaust and the smaller carb jet. As it stands it is claimed to becapable of 110 miles/gallon!The torque is quoted as 1.03 K.m/rpm and as it maxes at 8500, the max torqueis roughly 8500 k.m.Anyway, I've now found a UK based company that will cut me an alloy sprocket(not that expensive really) and I'll put it on and see..Tony.

Now then I had a cruise 2 in 2003 to 2004. You need a heavier weight fork oil in the front. Some air filer box restrictions definitely apply, easy to drill out and remain discreet however. Do change those carb jets, but don't overdo it coz it will run crap at high revs. If you can afford to get it done professionally then this will be money well spent, it will be a one off job with your air filter, plug, valve clearances and ignition circuits checked and all being optimized.Sprocket combinations; 14/48 standard. I have used 15/48, 16/48, 14/44, 15/44 and 16/44. Personally I thought 16/48 was the best combination. DO NOT go too small a sprocket on the rear, you will just cause yourself a load of work and hassle. Oh and change that shitty chain coz stretching chains wear sprockets out and not the other way round. It really should be one of the very first things you do on receiving the bike. Buy a good one that is suitable for more powerful machines, in the order of 60 - 70 quid ought to do it. CLEAN AND LUBRICATE IT REGULARLY. If you don't look after it. Then it will break on some horrible dark night on some nasty back road in the middle of nowhere. Be warned !The engine is a Suzuki GN125, so you will need an oil filter or two, shelved for oil changes. Use the best oil you can afford, it pays long term. Yes get a better plug, try a platinum tip or gold palladium; your tuning shop will know best.55/60w bulb in the front light, seeing is believing.Keep a close eye on that rear break cable it can get a bit iffy, as in fray.Get away from all those teccy numbers, point "0" this and 0.05% here is nothing. Its how the bike feels and responds.All engines peak and troughout their rev range, don't get bogged down with "peak figures" you wont be up there for most of the time.So 16/44 it is then ( yep I weighed 125 kg too ), the bike will be great.